Design Arguments: Old and New

The Design Argument

There are two broad forms of the design argument:

1.The Classical (“Old School”) Design Argument:

Paley’s is the most important version of the classical design argument. This version is an argument from analogy. It typically appeals to living organisms and their parts as cases of apparent design. The line of reasoning here can be put as follows:

We come to learn through experience whether an object has been intelligently designed. How do we learn to detect design? Well, over a long course of experience, we notice a constant conjunction of a cause of one type (intelligent designers) producing an effect of a certain type (complex objects whose parts work together to perform a function). Thus, after a while, we no longer have to observe a person designing an object in order to know that the latter has been designed. Rather, we can then legitimately *infer* that, say, a watch was fashioned by an intelligent cause. For we can then justifiably base such an inference on an inductive argument based on the observed constant conjunction of the cause-type of intelligence and the effect-type of complex objects whose parts work together to perform a function.

Now for the punchline. If we have come to know, via uniform experience, of this constant conjunction of intelligent causes producing the effect of complex objects whose parts work together to perform a function, then what must we conclude about living organisms and their parts -- things such as the marvelously intricate structures of cells, eyes, bird's wings, whole organisms, and even whole ecosystems? For these resemble the artifacts that we know to be designed, in that they, too, are incredibly complex entities whose parts work together to perform a function. For Pete's sake, think of the workings of a cell! We now know that it's functionally equivalent to (in the words of Michael Denton) "a self-replicating machine factory"! Thus, since living things relevantly resemble human artifacts, and the latter are intelligently designed, then we can't rationally avoid concluding that the former are intelligently designed as well.

In short, our basis for thinking that objects such as watches, cars, and computers are designed is an inductive inference based on our experience of a constant conjunction of a certain type of cause (intelligence) and a cerain type of effect (complex objects whose parts work together to perform a function). And our grounds for thinking that living organisms and their parts are designed is based on an argument from analogy between watches, cars, and computers on the one hand, and living organisms and their parts on the other.

The argument can be expressed as follows:

1. Human artifacts are intelligently designed.
2. Living organisms and their parts relevantly resemble human artifacts (in that they both are complex and their parts that work together to perform a function).
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3. Therefore, probably, living organisms and their parts are intelligently designed as well.

This form of the design argument is seldom used today, due to a number of criticisms. But the most forceful criticisms come from David Hume (see his masterful Dialogues Concerning Natural Religion), and Charles Darwin.

Some of Hume's most forceful criticisms are these: (i) since the argument is an argument from analogy, the likelihood of the conclusion turns one the degree of similarity between the two things compared in the premises. Unfortunately, the degree of similarity between artifacts and organisms is too low to warrant a confident inference to the intelligent design of the latter; (ii) even if they were simillar enough to infer design, the conclusion wouldn''t justify an inference to full-blown theism -- let alone orthodox Christian theism. Thus, even if the argument worked, it wouldn't show that the designer is immaterial, all-powerful, all-knowing, perfectly good, or even that there is just one designer; nor would it show that the designer is the creator and/or sustainer of the universe -- or even that the designer still exists.


But the most forceful criticism appears to be the one from Darwin -- i.e. the strong empirical evidence for biological evolution. If biological evolution is true, then the complex, apparently purposive structures and organisms we find in the biological realm don't require explanation in terms of (at least) the direct causation of a divine designer (although we'd need another explanation of the *origin* of living organisms, since the latter wasn't the result of mutation and natural selection. Whether there is or could be a natural explanation for the origin of living things, I don't pretend to know).

However, philosophers have come up with a new version of the design argument, one that doesn't fall prey to most of these objections, viz.:


2. The Contemporary (“New School”) Design Argument:

This version is not an argument from an analogy, but rather an abductive inference to the best explanation (and thus isn't subject to the "weak analogy" objection). For purposes of simplicity of discussion, we can say that, roughly, one hypothesis H1 is a better explanation of a range of data D than another hypothesis H2 if we would *expect* D more if H1 were true than we would if H2 were true.

According to this version of the design argument, then, certain features of the universe are treated as data, and then various hypotheses are offered to explain the data. It typically appeals to non-living aspects of the universe as cases of apparent design (and thus isn't subject to the "evolution" objection). The most common sorts of phenomena appealed to in such arguments is the range of fundamental constants of nature -- in particular, the extremely precise values they have, and must have in order for life to arise in the universe.

There are anywhere from 20 to 50 (or so) such features of the basic structure of the universe. Each of these has to have a mind-bogglingly precise numerical value in order for life to evolve in the universe. The following is a small sampling of these features:

-the strong nuclear force: this is the force that binds protons and neutrons together within the nucleus of the atom.

-If the strengthened or weakened by 1% or more: would reduce the amount of carbon and oxygen produced by stars, so that carbon-based life would not be possible; nor would any oxygen-breathing organisms be able to exist.

-the weak nuclear force: this force controls, among other things, the fusion of protons. It’s current strength prevents stars from exploding, and allows them to burn slowly.

-if slightly weaker: stars wouldn’t produce the requisite light, heat, and heavy elements. The universe would be largely composed of just helium

-if slightly stronger: stars wouldn’t produce the heavy elements

-the cosmological constant: this constant relates to the rate of expansion of the universe due to the Big Bang.

-If expansion rate were increased by more than one part in 10120: matter couldn’t clump together to form galaxies. This would mean no stars, which would mean no planets, and thus no habitat for life to exist

-If the expansion rate were decreased by more than one part in 10120: all of the matter in the universe would clump together into one giant clump before the relevant types of stars could form

-other examples include the strength of gravity, the mass of a proton, the fine structure constant, the electromagnetic force constant, and the total density of the universe.

If the numerical values of these, and any of the other constants, were increased or decreased – often just by a fraction – then no life at all could have arisen in the universe. Thus, it looks as though the basic structure of the universe has been “fine-tuned” in order for life to evolve within it.


The two hypotheses typically proposed to explain the data of fine-tuning above are (i) intelligent design and (ii) non-intelligent, natural causes. Thus, the Best Explanation version of the design argument can be expressed as follows.

Let ‘D’ denote some range of phenomena or data that needs explaining. For example:

D: The universe is fine-tuned for the existence of life (i.e., there are a large number of fundamental constants of nature. The value had by each of these is contingent, and independent the others. Each value is just one among an extremely large range of possible values, and each constant had to be assigned the value it has (or one very, very close to it) or no life would have arisen in the universe.)

Let ‘H1’ and ‘H2’ denote competing hypotheses offered to explain D:

H1: The fine-tuning of the universe is due to intelligent design.
H2: The fine-tuning of the universe is due to non-intelligent factors, such as chance and necessity.

Then we can state the abductive, inference-to-the-best-explanation version of the fine-tuning argument simply as follows:

1. The truth of H1 would lead us to expect D, but the truth of H2 wouldn’t lead us to expect D.
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2. Therefore, H1 is a better explanation of D than H2.